I use Milanote. You can find them here: www.milanote.com
They are basically a big digital corkboard that you can use to not only create mood boards, but you can link the board to external links for quick reference. Or you can copy and paste photos SUPER easily.
You can have reference photos/ a mood board of a city, some text blocks of info about it, links to some external NPC statblocks you want to reference, and then have subfolders in there that detail different places. I.e...you can have a subfolder of a tavern in the area, and doubleclick the folder and open an entirely new mood board that is JUST for this tavern.
Super fun.
Also, shameless plug, I have this video for new DM's :) Hopefully it helps.
It's called Milanote!
I created boards for my dress, flowers, cake, etc. It's super easy. Kinda like creating a webpage for them but you can drag the images all around the page and add text.
This online app might be what you are looking for https://www.milanote.com/refer/rcCjz86zkxDHkJ7wUD
There's also Prowritingaid.com that has amazing tools to help you write like a pro.
It depends on what kind of Story you want to tell with it. Start with that.
For example, i wanted a story about a Female Knight that rescues a princess from a Tower/Castle from a Badass Villainess, but more a la The Raid: Redemption style. From there i built the Magic System, from which i built the Social Structures, and so on, all that in a way that would serve me to tell that story.
A useful free online tool to help keep track of all your Worldbuilding notes is https://www.milanote.com/refer/rcCjz86zkxDHkJ7wUD
Come to think of it a lot of the interesting things in Evernote, they do in the backend.
I think if you want something more frontend heavy, look at 'cloning' milanote.
Milanote is basically like a free-form canvas where you can place notes, pictures etc.. - https://www.milanote.com/